Over a period of 14 months, we obtained nasal and throat swabs for virological examinations from patients, admitted to hospital with suspected pneumonia. Fifty-five cases of perihilar bronchitis and 103 cases of pneumonia were diagnosed based on radiological criteria. In 36% (n = 57) of the children, a pathogen could be determined by antigen ELISA. We found the following spectrum: Respiratory syncytial virus: 42%; Influenza A: 8%; Influenza B: 10%; Parainfluenza 1: 3%; Parainfluenza 2: 10%; Parainfluenza 3: 2%; Chlamydia: 17%; and Mycoplasma pneumoniae (serology only): 7%. In a control group of 59 healthy children, only one child showed a pathogen. In the past, viruses and Chlamydia have been underestimated as causes of lower respiratory tract infections. Antigen determination by ELISA has proved to be a reliable and rapid method for their detection.